The field of this invention relates to methods for breaking coal.
Coal found in the natural state generally exists as massive solid beds. According to usual coal mining procedures, the coal is broken into pieces of manageable size by the use of explosives, picks or other mechanical means, and finally removed from the coal bed mostly in the form of large lumps. These large lumps of coal are further reduced in size by breaking them down by mechanical procedures such as crushing, milling, grinding, pulverizing, etc. The degree of reduction in size is suited to the application for which the coal is to be used.
These physical methods for breaking coal, however, present certain disadvantages. For example, all of these methods are normally used in conjunction with each other and require a substantial energy expenditure including man power. Since numerous industrial processes which consume coal use the extracted product in a particulate form which requires a 1/2 inch top size or less, several size reduction operations can be required. Each of these subsequent processes employed for further particle size reduction requires specialized machinery and large additional expenditures of energy. In addition, such processes can produce large volumes of coal dust which is known to be hazardous due to its explosive nature and the effect on the health of workers carrying out the operations.
Another disadvantage of physical methods of reducing the particle size of coal is that the particle size of rocks and mineral impurities (for example, pyrite) can also be reduced. Size reduction of these impurities can inhibit the separation of these impurities from the coal in some physical separation procedures.
Heretofore, it has been recognized that physical methods of comminuting coal are not wholly satisfactory. For example, U.S. Pat. No. 3,870,237 to Aldrich issued Mar. 11, 1975 discloses a method for comminuting coal chemically involving treating the coal with liquid ammonia. While this method is interesting, it too presents several disadvantages. For example, the boiling point of liquid ammonia is quite low, namely, -33.degree. C. This is a disadvantage because as the boiling point of normally gaseous liquids decreases, the liquids become more difficult to handle. Another disadvantage of ammonia is that it can react with coal. If this should occur, the treated coal would release nitrogen oxide pollutants to the atmosphere on burning.
A more desirable coal comminution process would not require physical comminution and would overcome the abovementioned disadvantages of comminution associated with ammonia.